Why can newborn infants have low levels of vitamin K?

Newborn infants often have low levels of vitamin K due to several physiological factors. Primarily, infants are born with an absence of the intestinal bacteria that typically synthesize the majority of the vitamin K required by mammals. Additionally, newborns often lack sufficient body stores of the vitamin, and breast milk contains only low levels of it.1

Furthermore, there is poor transport of vitamin K across the placenta during pregnancy, which limits the amount an infant receives before birth. These combined factors can lead to a condition known as hemorrhagic disease of the newborn, characterized by spontaneous internal or external bleeding. To protect against this, it is standard medical practice to administer vitamin K to infants shortly after birth.231